[例3-9]输入月份,打印1999年该月有几天。 程序如下: #include main() { int month. int day. printf("please input the month number:"). scanf("%d",&.month). switch(month) { case 1: case 3: case 5: case 7: case 8: case 10: case 12:day=31. break. case 4: case 6: case 9: case 11:day=30. break. case 2:day=28. break. default:day=-1. } if day=-1 printf("Invalid month input !\n"). else printf("1999.%dhasÝ.ays\n",month,day). }